This invention relates generally to an armature assembly for a selectively engagable and disengagable coupling such as an electromagnetic clutch or brake.
Newton U.S. Pat. No. 4,493,407, hereby incorporated by reference, discloses a typical electromagnetic clutch in which a slotted armature disc is connected to a driven hub by a mounting plate and is adapted to be attracted into engagement with a driving rotor when an electromagnet is energized. The armature disc is connected to the mounting plate by a series of leaf springs which couple the armature disc in the mounting plate for rotation in unison while allowing the armature disc to move toward and away from the rotor when the electromagnet is energized and de-energized.
Another type of armature assembly is disclosed in Booth U.S. Pat. No. 5,150,779, also hereby incorporated by reference. In that armature assembly, a resiliently yieldable plastic web acts to connect a low magnetic reluctance armature disc for rotation with the driven hub. The web flexes axially in order to permit the armature disc to move toward and away from the rotor when the clutch is engaged and disengaged.
One problem, however, is that impact noise is produced when the armature disc is initially snapped into engagement with the rotor. Noise is also produced by vibration which occurs during slippage of the armature disc and when the disc is disengaged from the rotor.
Van Laningham, et al., U.S. Pat. No. 5,372,228, also incorporated by reference discloses an electromagnetic clutch in which an annulus of sound damping material is sandwiched between an armature disc and a backing ring. The annulus and the backing ring coact to define a constrained-layer damping system for reducing noise when the armature disc is snapped into engagement with the rotor of the clutch and also during slipping and disengagement of the armature disc. However, this approach increases an axial length of the electromagnetic coupling, and the backing disc adds weight to the overall device.
Accordingly, there is a need to provide an improved electromagnetic coupling that minimizes or eliminates one or more of the problems as set forth above.
A general object of the present invention is to provide a new and improved armature assembly in which the level of noise produced by during initial engagement of the armature and during slippage and disengagement is reduced.
This and other objects are achieved by an armature assembly in which an annulus of sound damping material is sandwiched and compressed between the armature disc and a web portion of a hub assembly wherein the web portion is generally rigid but is axially movable relative to a hub of the hub assembly. The web serves as a constraining layer to cause sheer strains to develop in the damping material and to cause noise to be dissipated as a result of sheer deformation of the damping material.
The armature assembly of the present invention also has the advantage of having a reduced axial length relative to prior armature assemblies incorporating constrained-layer damping techniques. In addition, the armature assembly in accordance with the invention also has a reduced weight relative to prior armature assemblies incorporating constrained-layer damping techniques, since no backing plate is used.